Nucleation of polypropylene

ABSTRACT

THE CRYSTAL STRUCTURE OF PROPYLENE POLYMERS IS ALTERED BY THE ADDITION OF A SMALL CONCENTRATION OF A COMPOUND SELECTED FROM THE THOSE COMPOUNDS OF THE FORMULAS   2-(X=),4-R,5-R&#39;&#39;-1,2,3,4-TETRAHYDROPYRIMIDIN-6(5H)-ONE WHEREIN R&#34; IS A HYDROGEN ATOM OR AN ALKYL, ARYL OR CYCLOALKYL RADICAL HAVING FROM 1 TO 12 CARBON ATOMS THEREIN.   2-HO,4,6-BIS(R&#34;-HN-)PYRIMIDINE   WHEREIN X IS O OR S, AND R OR R&#39;&#39; IS A HYDROGEN ATOM OR A METHYL, ETHYL, PROPYL, ISOPROPYL OR A CARBOXYL GROUP; OR

United States Patent 01 ifice 3,563,971 NUCLEATION OF POLYPROPYLENEHarold V. Wood and Terry D. Brown, Bartlesville, Okla,

assignors to Phillips Petroleum Company, a corporation of Delaware NoDrawing. Filed Sept. 26, 1968, Ser. No. 762,970 Int. Cl. C08f 3/08, 3/10U.S. Cl. 260-935 9 Claims ABSTRACT OF THE DISCLOSURE The crystalstructure of propylene polymers is altered by the addition of a smallconcentration of a compound selected from those compounds of theformulas This invention relates to the nucleation of propylene polymers.

Frequently it has been found desirable to modify the crystallinestructure of the various olefin polymers. In particular with suchrelatively new members of this class of polymers as high densitypolyethylene and polypropylene, it has been found possible to greatlyalter the physical properties by adding various materials to the polymerto nucleate the formation of crystals. This is because in many of thesepolymers, large crystal structures known as spherulites form on coolingthe polymers to a point below their crystalline freezing point. Theaddition of nucleating agents results in the formation of a crystalstructure which is substantially free of large spherulites. This resultsin a polymer with physical properties which are better suited forcertain applications. For instance, it results in a polymer havinggreater transparency which is desirable in many film applications. Alsoit results in a polymer of increased flexural modulus or stifiness whichmakes possible the fabrication of parts of thinner crosssection havingrigidity comparable to those made from thicker sections of polymer notcontaining a nucleating agent.

Several materials have been disclosed in the prior art as being ofvarying degrees of value as nucleating agents for certain polymers.While some effort has been made to characterize the type of agents whichare effectivesee for instance I. Polymer Science, vol. 39, page 544(l959)--for the most part the reasons some materials are eifective andothers are ineifective has gone unexplained except that it is generallythought that the nucleating agent must have a higher melting point thanthe base polymer so that it can provide solid particles around which thepolymer crystals can form. Some materials will func tion as nucleatingagents for polypropylene, for instance,

but are ineffective in polyethylene. Materials proposed to 3,563,971Patented Feb. 16, 1971 date as nucleating agents include certain finelydivided inorganic materials, polycarboxylic acids and even otherpolymers.

It is an object of this invention to provide propylene polymers withimproved physical properties.

It is a further object of this invention to provide propylene polymerswith improved optical properties.

It is a still further object of this invention to provide propylenepolymers with increased fiexural modulus.

It is a further object of this invention to provide propylene polymercompositions suitable for fabricating into products of improved opticaland other physical properties.

Other aspects, objects, and the several advantages of the invention areapparent from a study of the disclosure and appended claims.

In accordance with the present invention, we have discovered thatcompounds of the formulas wherein X is O or S, and R or R' is a hydrogenatom or a methyl, ethyl, propyl, isopropyl or a carboxyl group; or

wherein R" is a hydrogen atom or an alkyl, aryl or cycloalkyl orcombinations thereof such as alkaryl, alkylcycloalkyl, etc. radicalhaving from 1 to 12 carbon atoms therein, function as nucleating agentsto provide an improved propylene polymer composition.

Examples of suitable compounds of the Formula (A) are 2-thiouracil6-methyl-2-thiouracil 2-thiouracil-6-carboxylic acid Uracil6-methyluracil 5,6-diethyl-2-thiouracil 5,6-diisopropyl-2-thiouracilUracil-6-carboxylic acid, and S-methyl-uracil-6-carboxylic acid.

Illustrative examples of suitable compounds of the Formula (B) are4,6-bis(ethylamino)-s-triazine-2-ol 4,6-diamino-s-triazine-2-ol4-ethylamino-6-amino-s-triazine-2-ol 4,6-bis(isopropylamino)-s-triazine-2-ol4-cyclohexylamino-6-amino-s-triazine-2-ol4-ethylamino-6-propylamino-s-triazine-2-ol4-dodecylamino-6-amino-s-triazine2-ol 4,6-bis( dodecylamino-s-triazine-2-ol 4,6-bis phenyl amino s-triazine-2-ol 4,6-bis(methylcyclohexylamino -s-triazine-2-ol, and 4,6-bis (phenylbutylamino-s-triazine2-ol.

Applicable polymers for use in the practiceof this invention includehomopolymers and copolymers of propylene. These polymers can be producedby any of the methods well known in the art. A particularly suitablepolymerization method for preparing olefin polymers and copolymers foruse in the instant invention is that described in US. 2,825,721 to Hoganet al. Another suitable method for preparing olefin polymers andcopolymers for use in the instant invention is that utilizing thewell-known organometal catalyst systems comprising a transition metalcompound such as a titanium halide and a reducing compound such as analuminum alkyl.

The nucleating agents can be incorporated into the polymers by any knownmanner such as by melt blending, dry blending or solution blending. Theconcentration of additive can be very low for instance between 0.005 and1 weight percent based upon the weight of the polymer, preferablybetween 0.01 and 0.1 weight percent.

In order to effect the modification of crystal structure the polymermust be crystallized from the melt phase. If melt blending is used, thenthe modified crystal structure will result on the initial cooling. If atechnique such as dry blending is used, the polymer must be melted andthen recrystallized; this is of no disadvantage however since thepolymer will be generally melted during the fabrication step. Of coursethe polymer can be melted and recrystallized a number of times ifdesired.

The polymer can contain other additives such as antioxidants, UVstabilizers, pigments and the like.

The following examples will further illustrate the invention.

EXAMPLE I A pelletized polypropylene having a melt fiow 6.20 andstabilized with 0.15 weight percent 2,6-di-tert-butyl-4- methylphenoland 0.15 weight percent dilaurylthiodipropionate was dry blended withthe nucleating agents. The blend was masticated in a plastograph forfive minutes at 190 F. at 50 r.p.m. under nitrogen. Test samples weremolded at 425 F. The results are tabulated below.

TABLE I Flex. DTA "C. Melt mod. Sample No. Flow MP FP Additive .2% wt.

1 (Control)-.- 6. 212 163 116 None. 2 4. 63 245 162 1294,6-vis(ethylamino)-s-triazzine-2-0l.

A homoploymer of proplyene, containing 0.15 part by weight2,6-di-tert-butyl-4-methylphenol and 0.15 part by weightdilaurylthiodipropionate was used. Except for the control, the polymerand the nucleating agents listed below were dry blended and thenmasticated in a plastograph for five minutes at 190 C., 50 r.p.m. undernitrogen. Test samples were molded at 425 F. The results are tabulatedbelow.

TABLE II DTA C. 0 Melt Flex. Sample No. ilow mod. MP FP Additive 1(Control).-. 6. 20 212 163 116 None. 2 4. 78 215 164 122 0.2%2-thiouracil.

4. 66 238 163 128 0.2% 6-methy1-2-thionracil. 5.45 228 164 122 0.2%2-thiouracil-6-carboxylic acid. 4. 42 220 162 123 0.2% uracil.

u ASTM D 1238-62T, Condition L. b ASTM D 790-63. By differential thermalanalysis.

It is readily apparent that the additives improve the nucleationproperties of polypropylene, as shown by the increase in freezing pointand simultaneously increase the flexural modulus which is desirable inthe production of shaped articles from the polymer. The improvedmicrostructure of the polymer also improves the clarity of the shapedarticles.

Reasonable variations and modifications are possible within the scope ofthis disclosure without departing from the spirit and scope thereof.

We claim:

1. A nucleated composition comprising a polymer of propylene and from0.005 to 1.0 weight percent, based on the weight of said polymer of anucleating compound 10 selected from the group consisting of (a)compounds of the formula N RIIN(!,I/ \C1OH n' HR wherein R" is ahydrogen atom or an alkyl, aryl or cycloalkyl radical having from 1 to12 carbon atoms therein.

2. A composition according to claim 1 wherein said nucleating compoundis a compound of the formula wherein X is O or S and R or R is ahydrogen atom or a methyl, ethyl, propyl isopropyl or a carboxyl group.

3. A composition according to claim 1 wherein said nucleating compoundis a compound of the formula wherein R is a hydrogen atom or an alkyl,aryl or cycloalkyl radical having from 1 to 12 carbon atoms therein.

4. A composition according to claim 2 wherein said agent is2-thiouracil.

5. A composition according to claim 2 wherein said agent is6-methyl-2-thiouracil.

6. A composition according to claim 2 wherein said agent is2-thiouracil-6-carboxylic acid.

7. A composition according to claim 2 wherein said N agent is uracil. H

8. A composition according to claim 3 wherein said R (|7 0H agent is4-6-bis(ethylamino -s-triazine-2-o1. N

9. A method for modifying the crystal structure of 5 polymers ofproplylene comprising: admixing with said I polymer between 0.005 and1.0 weight percent, based on the weight of the polymer, of a nucleatingagent sewherein is a hydrogen atom or an alkyl aryl or lected fromthoseof the formula cycloalkyl radical having from 1 to 12 carbon atoms 10therein; and crystallizing the resulting mixture from a 0 melt phase. IReferences Cited UNITED STATES PATENTS 'B g 1 3,207,735 9/1965 Wijgazen-93.7 3,268,499 8/1966 Wales 26093.7

LII JOSEPH L. SCHOFER, Primary Examiner W. F. HAMROCK, AssistantExaminer wherein X is O or S and R or R is a hydrogen atom or 20 amethyl, ethyl, propyl, isopropyl or a carboxyl group; U.S. Cl.X.R. andthose of the formula 260-94.9, 96

